Method of sizing of fibers and articles manufactured from the same

ABSTRACT

The method includes the steps of functionalizing a polyaryletherketone (PAEK) polymer, and blending the PAEK polymer with water to form a sizing composition. The method may further include the step of applying the sizing composition to a fiber. The method may further include the step of heating the fibers, coated with sizing composition, for example to between 300C-400C. In some methods, the functionalized PAEK polymer comprises functionalized polyetherketoneketone (PEKK). In yet other methods, the functionalized PAEK polymer comprises sulfonated PEKK (sPEKK).

FIELD OF THE INVENTION

The present invention relates to a method of sizing fibers and articlesmanufactured from the same. More specifically, the present inventionrelates to a method of applying a functionalized PAEK polymer coating toa fiber.

BACKGROUND OF THE INVENTION

It is known to apply various chemical treatments to fibers such as glassfibers and carbon fibers to facilitate handling of the fibers, improveprocessability for compounding and downstream processes such asinjection molding, and to improve strength and other properties forspecific end-use applications. A surface treatment, which may also bereferred to as a coating composition, sizing composition, or sizingmaterial, may be applied to at least a portion of a surface of a fiberto protect it from abrasion and to assist in processing. This process ofapplying the surface treatment is commonly referred to as sizing.

In one known process, a sizing material is applied to a target material,for example a plurality of fibers, using a solvent. First, the sizingmaterial is dissolved in the solvent. Next, the solvent is applied tothe fibers so that the sizing material is applied to at least a portionof a surface of the fibers. After the solvent is applied to the fibers,the fibers coated with sizing material are heated to evaporate thesolvent.

Polyaryletherketones (PAEK) polymers are of interest to use as sizingsfor fibers used as reinforcements for plastic type materials—especiallythose processed at higher temperatures than can be tolerated by morecommon sizings. A PAEK polymer powder may be from the group consistingof polyetheretherketone (PEEK), polyetherketoneketone (PEKK),polyetherketone (PEK), polyetheretherketoneketone (PEEKK) orpolyetherketoneetherketoneketone (PEKEKK).

U.S. Patent Application No. 2011/0294943 (the '943 application)discloses a method of applying amorphous (i.e. non-crystalline) PAEK asa sizing composition to fibers. The '943 application recognizes thatmany polymeric resins, especially highly crystalline engineeringthermoplastics such as crystalline PAEK, do not exhibit good adhesion tovarious fiber surfaces. To overcome this problem, the '943 applicationproposes a method of coating a fiber with amorphous PEKK. The disclosureof the '943 application is incorporated herein in its entirety.

A disadvantage of the method disclosed in the '943 application is thatit requires aggressive, toxic, and potentially explosive solvents todissolve the amorphous PAEK. The need to use such dangerous solventsgreatly inhibits broader adoption and use of sizing compositionscomprising amorphous PAEK. The '943 application, for example, teachesdissolving a PAEK resin using methylene chloride or concentratedsulfuric acid to create a solution for sizing a fiber. Such wetting anddoctoring processes are well known and, therefore, are not detailedherein except to note that they require highly corrosive solvents thatare not commonly used for reasons of safety, environment and machinerylifetime. Due to the low solubility of PAEK resins in any solventsystem, this process must of necessity create copious volumes ofdifficult (toxic, acidic) to manage waste. As a result, such processesare expensive and dangerous, limiting their usefulness and discouragingadoption by industry.

What is desired, therefore, is to provide a system and method ofapplying a sizing comprising a PAEK polymer to a fiber in which a lessvolatile solvent, as compared to known methods, is used.

SUMMARY OF THE INVENTION

The present invention resides in one aspect in an improved method ofsizing a fiber. The method includes the steps of functionalizing a PAEKpolymer, and blending the PAEK polymer with water to form a sizingcomposition. The method may further include the step of applying thesizing composition to a fiber. The method may further include the stepof heating the fibers, coated with sizing composition, for example tobetween 300° C.-400° C. to defunctionalized the applied coating.

In some embodiments of the present invention the step of functionalizingthe PAEK polymer comprises sulfonation. In yet other embodiments of thepresent invention, the PAEK polymer comprises polyetherketoneketone(PEKK). In yet further embodiments of the present invention, the methodincludes the step of heating the applied sizing composition to evaporatethe water.

In some embodiments of the present invention, the method includes thestep of heating the applied sizing composition to a temperature at orabove a defunctionalization temperature of the applied sizingcomposition. Further embodiments of the present invention include thestep of heating the applied sizing composition to a temperature at orabove a fusion temperature of the applied sizing composition.

In some embodiments of the present invention, the functionalized PAEKpolymer is dissolved in a solvent other than water. Such solvents mayinclude, but are not limited to, various alcohols, acetone, volatileorganic oils, and other non-volatile solvents known in the art.

DETAILED DESCRIPTION OF THE INVENTION

First, a PAEK polymer is functionalized. In functionalizing the polymer,certain chemical groups are added to the basic structure of themolecule. The functionalization step alters the wetting and solubilitybehaviors of the polymer. For example, by functionalizing a PAEK familymaterial, it is possible to make the material water soluble. Thefunctionalized PAEK polymer is blended with water to form a sizingcomposition.

An example of a functionalization for use with the present inventionincludes, but is not limited to sulfonation. Sulfonation of a PAEKmaterial results in a PAEK material that is soluble in water. It ispossible to vary functionalization of the PAEK material so as to varythe solubility. In some embodiments, the functionalized PAEK material issoluble to the point of deliquescence. The functionalization step can beperformed on the PAEK material after polymerization or in the syntheticpath. After the PAEK material is functionalized, it is blended withwater to form the sizing composition. It is possible to vary theviscosity of the sizing composition by adjusting the ratio offunctionalized PAEK material to water.

In one embodiment of the present invention, amorphous PEKK isfunctionalized to form sPEKK. The sPEKK is blended with water to form asizing composition. Suitable amorphous polyetherketoneketones areavailable from commercial sources, such as, for example, certain of thepolyetherketoneketones sold under the brand name OXPEKK by OxfordPerformance Materials, South Windsor, Conn., including OXPEKK-SPpolyetherketoneketone. The sizing composition may additionally includecomponents other than the sPEKK, such as stabilizers, pigments,processing aids, fillers, and the like.

The sizing composition resulting from the functionalized PAEK and thewater is relatively benign and readily managed. The sizing compositionmay be applied to fiber or other materials using known methods andsystems. The present invention is useful in connection with any type offiber, but particularly fibers that are to be used as reinforcements orfillers in polymeric matrices. Suitable fibers include, for example,glass fibers, carbon fibers, polymeric fibers, metallic fibers, mineral(ceramic, inorganic) fibers and the like. Glass fibers (fiberglass) maybe obtained from any type of glass, e.g., A glass, E glass, S glass, orD glass. Carbon fibers (which include graphite fibers) are typicallyprepared by pyrolysis of organic or polymeric fibers (such as PAN).Polymeric fibers include fibers made from any of the known types ofthermoplastic polymers such as polyamides, polyolefins, polyaramids,polyesters, poly(p-phenylene-2,6-benzobisoxazole)(PBO), and the like.Suitable metallic fibers include fibers prepared using any type of metalor metal alloy, such as iron, steel, aluminum, aluminum alloys, copper,titanium, nickel, gold, silver and the like. Mineral fibers that can beused in the present invention are fibers made from natural or syntheticminerals, refractory oxides or metal oxides and include, but are notlimited to, mineral wool, rock wool, stone wool, basalt fibers, aluminafibers, beryllia fibers, magnesia fibers, thoria fibers, zirconiafibers, silicon carbide fibers, quartz fibers, boron fibers, asbestosfibers and high silica fibers and the like.

Fibers of any diameter or length may be sized with a coating offunctionalized PAEK and water in accordance with the present invention.For example, the fiber may be from 1 micron to 1 mm in diameter.Typically, the fiber is many times longer than its diameter. Forexample, the fiber length may be at least 10, 100, 1000 or 10,000 timesthe fiber diameter.

After an application is applied, it is heated. Sufficient heat isapplied so that the sizing composition dries and creates a solid layeron at least a portion of a surface of the fiber. At this point, theapplied sizing composition is still water soluble as before theapplication because the applied PAEK is functionalized. The applied PAEKpreferably forms a relatively thin coating on the fiber surface. Forexample, the coating may be from about 1 to about 50 microns thick. Inone embodiment of the invention, the fiber surfaces are completelycovered by the coating, although in other embodiments certain portionsof the fiber surfaces remain uncoated. Typically, the coating maycomprise from about 0.01 to about 10% by weight of the sized fibers.

Some embodiments of the present invention include the step of heatingthe applied sizing composition to a temperature at or above thedefunctionalization temperature of the PAEK polymer, for example inreference to sPEKK to between 300° C.-400° C. This heating causes thefunctional groups to detach from the PAEK polymer, resulting in anapplied sizing composition that is less water soluble. In this way, itis possible to recover the desirable solvent resistant behaviors in theoriginal polymer after it has been applied to the fiber.

In some embodiments, the applied sizing composition is heated to atemperature at or above the fusion point of the PAEK polymer, therebyenhancing the bonds of certain systems.

Means for applying the sizing composition include, but are not limitedto, pads, sprayers, rollers or immersion baths, which allow asubstantial amount of the surfaces of the individual filaments of thefiber to be wetted with the sizing composition. The sizing compositionmay be applied to the fibers by dipping, spraying, roll coating,extruding, pultrusion, or the like. In one embodiment, the sizingcomposition is applied to the fibers continuously.

In one embodiment of the invention, chopped fibers sized in accordancewith the present invention may be mixed with a polymeric resin andsupplied to a compression- or injection-molding machine to be formedinto fiber-reinforced composites. Typically, the chopped fibers aremixed with pellets of a thermoplastic polymer resin in an extruder. Forexample, polymer pellets can be fed into a first port of a twin screwextruder and the chopped sized fibers then fed into a second port of theextruder with the melted polymer to form a fiber/resin mixture.Alternatively, the polymer pellets and chopped fibers can be dry mixedand fed together into a single screw extruder where the resin is meltedand the fibers are dispersed throughout the molten resin to form afiber/resin mixture. Next, the fiber/resin mixture is degassed andformed into pellets. The fiber/resin pellets can then be fed to amolding machine and formed into molded composite articles that have asubstantially homogeneous dispersion of fibers throughout the compositearticle.

The sized fibers of the present invention may also be used in long-fiberthermoplastic applications. Fiber-reinforced thermoplastic polymerstructural components can be manufactured from long fiber thermoplastic(LFT) granulates (pellets), glass mat thermoplastic (GMT) sheets, orpultruded sections wherein the fibers have been sized withfunctionalized amorphous polyetherketoneketone. Long fiber-reinforcedgranulates can comprise sized fiber bundles encapsulated with athermoplastic through a cable coating or a pultrusion process. The LFTgranulates, which contain fibers equal in length to the pellet, e.g., 1to 25 mm, can be injection molded, but can also be extrusion compressionmolded in order to preserve fiber length in the finished product.

Polymer components reinforced with sized fibers in accordance with thepresent invention may also be manufactured using continuous in-lineextrusion methods known in the art. Such methods involve theplastication of a polymer in a first single screw extruder from whichthe output is fed to a second single screw extruder. Fibers areintroduced in the polymer melt in the second extruder, either inchopped-segmented form or as continuous strands under a predeterminedtension. The fiber-reinforced polymer is fed into an accumulator andthen applied automatically or in a separate step to a compressionmolding tool wherein the fiber-reinforced polymer is shaped as requiredfor a particular application. Alternatively, the fiber-reinforcedpolymer may be continuously extruded onto a conveyor and sectionedthereupon. The conveyor delivers the sectioned fiber-reinforced polymerto a placement assembly which removes the sectioned material from theconveyor and places the material upon the compression molding tool.

The process of compounding and molding the sized reinforcing fiber andthe matrix resin to form a composite may be accomplished by any meansconventionally known in the art. Such compounding and molding meansinclude, but are not limited to, extrusion, wire coating, blow molding,compression molding, injection molding, extrusion-compression molding,extrusion-injection-compression molding, long fiber injection, andpushtrusion.

The orientation of the sized fibers within the polymeric matrix of thecomposite produced in accordance with the present invention may bevaried and controlled as desired using the techniques known to thoseskilled in the field. For example, the fibers may be continuous andaligned, or discontinuous and aligned, or discontinuous and randomlyoriented.

The amount of fiber included in the composite is generally about 1% toabout 90% by weight, based on the total weight of the compositeformulation.

The coating in accordance with the present invention improvescompatibility and adhesion with the resin matrix, and results incomposites with more desirable properties such as higher short-term andlong-term mechanical properties.

Reinforced polymers prepared in accordance with the present inventionmay be use in any of the end use applications where such materialsconventionally are employed or have been proposed to be employed.Representative applications include composites for aerospace/aircraft,automobiles and other vehicles, boats, machinery, heavy equipment,storage tanks, pipes, sports equipment, tools, biomedical devices(including devices to be implanted into the human body, such asload-bearing orthopedic implants), building components, and the like.Benefits of the invention described herein include higher tensilestrength, higher compressive strength, improved resistance to crackinitiation and propagation, greater creep resistance, and higherresistance to attack by various chemicals and solvents, as compared toreinforced polymers prepared using fibers that are not sized with acoating in accordance with the present invention.

Fiber-reinforced composites in accordance with the present inventioncan, for example, be used to prepare laminar panels that are stacked andbonded to each other or can be used as face sheets in the production ofsandwich panels having honeycomb or foamed cores.

EXAMPLE

Example 1: PEKK resin is sulfonated in a process involving warm,concentrated sulfuric acid (>98% wt acid in water, >30° C., <5% wtpolymer in acid) to yield an sPEKK (apx. 25% sulfonated) materialsoluble in warm water (˜50° C.). Using DSC it has been determined thatat the sPEKK de-functionalizes at approximately 260° C. At thattemperature, the acid groups are detached returning the material toPEKK. Repeat cycling shows change is permanent.

After the PEKK resin is sulfonated and dissolved in water forming thesizing composition, the sizing composition is applied to the fiber.After this application, the fiber coated with sizing composition isheated to between 300° C.-400° C., whereupon the applied PEKK isdefunctionalized and fuses to the fiber surface. Such fiber tows arereadily handled.

When the sPEKK was blended in water, the solvent displayed excellentwetting behavior against glass beaker walls and was well bonded to theDSC can after analysis. Dragging of glass fibers through solutionresulted in easy coating, tolerant of manipulation to encourage properinfiltration into the fiber bundle. Oven drying of the applied sizingcomposition at 150° C. resulted in reduced thickness of the appliedsizing composition however it did not impact its solubility. Forexample, the applied sizing composition was rinsed clean from the fibersusing water at approximately 90° C. Further heat treatment to fusion ofresin yielded a well bonded strand no longer water soluble even afterboiling for 1 hour.

Although the present invention has been disclosed and described withreference to certain embodiments thereof, it should be noted that othervariations and modifications may be made, and it is intended that thefollowing claims cover the variations and modifications within the truescope of the invention.

What is claimed is:
 1. A method of sizing a fiber comprising the stepsof: functionalizing a polyetherketoneketone (PEKK) polymer bysulfonation to form sPEKK; combining the sPEKK with water to form asizing composition; applying the sizing composition to the fiber;heating the sized fiber to approximately 150° C. to evaporate the waterin the applied sizing composition, wherein the sPEKK remains watersoluble after the step of heating to evaporate.
 2. The method of claim1, wherein the step of combining the sPEKK with water to form a sizingcomposition includes adjusting a ratio of the sPEKK to the water to varyviscosity of the sizing composition.
 3. The method of sizing fiberaccording to claim 1, wherein the step of functionalizing apolyetherketoneketone (PEKK) polymer by sulfonation to form sPEKK yieldssPEKK that is approximately 25% sulfonated.
 4. A method of sizing afiber comprising the steps of: functionalizing a polyetherketoneketone(PEKK) polymer by sulfonation to form sPEKK; combining the sPEKK withwater to form a sizing composition; applying the sizing composition tothe fiber; heating the applied sizing composition to a temperature at orabove the defunctionalization temperature of the sPEKK, wherein thetemperature causes functional groups to detach from the sPEKK.
 5. Amethod of sizing a fiber comprising the steps of: functionalizing apolyetherketoneketone (PEKK) polymer by sulfonation to form sPEKK;combining the sPEKK with water to form a sizing composition; applyingthe sizing composition to the fiber; wherein the step of functionalizinga polyetherketoneketone (PEKK) polymer by sulfonation to form sPEKKyields sPEKK that is approximately 25% sulfonated.
 6. The method ofclaim 5, comprising a step of heating the applied sizing composition toa temperature at or above the defunctionalization temperature of thesPEKK, wherein the temperature causes functional groups to detach fromthe sPEKK.
 7. The method of claim 5, further comprising a step ofheating the sized fiber to approximately 150° C. to evaporate the waterin the applied sizing composition.
 8. The method of claim 7, comprising,after the step the of heating the sized fiber to approximately 150° C.to evaporate the water in the applied sizing composition, a further stepof heating the applied sizing composition to a fusion point of thesPEKK, wherein the applied sizing composition is heated to between 300°C. and 400° C.
 9. The method of claim 8, wherein the step of heating theapplied sizing composition to a fusion point of the sPEKK causes one ormore functional groups to detach from the sPEKK.